Poly(hydrocarbylene aryl phosphate) compositions of the formula ##STR1## where Ar is either unsubstituted or substituted aryl, A is a hydrocarbylene bridging group comprising, for example, alkylene, arylene, two arylene groups joined by a bridging group (e.g., --C(CH.sub.3), --SO.sub.2 or --CO), or biarylene, and n is equal or greater than 1 are a known class of flame retardant. Such compositions typically are a blend of the "bis"phosphate, where n=1, and higher oligomers, where n is an integer greater than 1. The term "poly" is used herein to include both the "bis"phosphate composition as well as the higher oligomers.
One technique for formation of such compositions involves the initial reaction of a phosphorus oxyhalide (e.g., phosphorus oxytrichloride) with an aromatic diol (e.g., bisphenol A resorcinol or hydroquinone) followed by the reaction of the resulting reaction product with, for example, an aromatic hydroxy compound (e.g., phenol). Examples of this route are described in U.S. Pat. No. 2,520,090 and Japanese Patent Publication Nos. 89/31,544, 57/174,331 and 88/227,632. These routes are plagued by the large excess of phosphorus oxytrichloride needed to achieve a high content of dimer as product, for example, and the relatively long time needed to strip excess phosphorus oxytrichloride from the reaction vessel. Also, the stripping of phosphorus oxytrichloride from the reaction mixture prior to addition of phenol for long periods of time at relatively high temperatures, to lessen the ultimate amount of triphenyl phosphate, for example, that is present in the final product, can result in an undesired change in the desired composition which results.
While it is known to form compounds of the formula (ArO).sub.2 P(O)Cl (see U.S. Pat. No. 3,965,220), only a few disclosures are known to exist in which such polyphosphate compounds are formed in which the initial reaction is between monohydroxy compound and phosphorus oxychloride with the second reaction step using diol as the reagent. In U.S. Pat. No. 4,133,846 it is taught in Example 4 that bis(2-chloroethyl) chlorophosphate and pentaerythritol were to be reacted to form the desired product. Presumably, the bis(2-chloroethyl) chlorophosphate could be formed by reaction of phosphorus oxytrichloride and appropriate monohydroxy compound (i.e., 2-chloroethanol). U.S. Pat. No. 3,254,973, at Col. 5, line 66 and following, illustrates preparation of 4,4'-isopropylidene diphenol bis(di-o-tolylphosphate) by first reacting phosphorus oxychloride with o-cresol to form a reaction mixture in which di-o-tolyl phosphorochloridate cuts are removed by distillation. The di-o-tolyl phosphorochloridate from the first reaction step was then reacted with the diol (i.e., bisphenol A) to make the desired bisphosphate.